Polyvinyl acetate -cement compositions



United States Patent 2,733,995 POLYVINYL ACETATE CEMENT coMrosrrroNsWilliam D. Robinson, Niagara Falls, N. 1., assignor to E. I. du Pont deNemours and Company, Wilmington, Del., a corporation of Delaware N0Drawing. Application December 6, 1952, Serial No. 324,599

7 Claims. (Cl. 106-90) This invention relates to coatings suitable formasonry, particularly concrete, surfaces. More particularly it relatesto coating compositions or paints suitable for dispersion in water andcontaining water dispersible polyvinyl acetate and a hydraulic cement.

Paints made of cement and water have found utility both for protectiveand decorative coatings on masonry surfaces. These paints or coatingsare suspensions or dispersions of hydraulic cements, especially Portlandcement in water. The dispersions usually contain other solid additivesin addition to the cement such as pigments, hydrated lime, stearatesalts and the like. These coatings generally do not adhere well tosmooth dense masonry surfaces. Since a prime purpose of a coating onmasonry is to seal the surface against water and water vapor penetrationit is evident that poor bonding of the coat or paint to the surface isvery undesirable. Furthermore, these coatings are relatively verybrittle and this defect combined with shrinkage during the drying of thecoating results in the development of the fine checkings or cracks orcrazing which increases the moisture permeability of the resultantcoating.

Another great disadvantage of the cement-type of coatings is that theirapplication requires much care and labor to assure good results. Thesurface to be coated must be made thoroughly wet before applying thepaint. Then the painted surface must be kept damp or moist during thedrying and curing periods.

Polyvinyl acetate emulsions can be added to cement paints or coatingcompositions and this will eliminate the need for wetting the masonrysurface prior to application. However, the cement paints containing theaqueous polyvinyl acetate dispersions have poor shelf stability. Thecement components have an adverse effect on the protective colloids ordispersing agentsin the polyvinyl acetate dispersions.

Accordingly it is the objective of this invention to preparecement-water coating compositions which will have good shelf life in thedry form. It is another objective to produce compositions which onmixing or dispersing in water will permit the application to concrete ormasonry surfaces of coatings having superior properties of adhesion andplasticity and which therefore exhibit greater resistance to thepenetration of water or water vapor. A further objective is thepreparation of stable dry paint compositions which require only theaddition of water prior to applying them to masonry surfaces. Otherobjectives will become clear as the invention is further described.

It has been discovered that these objectives can generally be achievedby adding water dispersible dry poly vinyl acetate to the dry componentsof a hydraulic cement and any desired dry additives such as pigments.

Such mixtures have long shelf stability and on mixing with water can beapplied to dry masonry walls by simple painting operations. Theresulting coatings will dry and cure without the need of maintainingspecial moisture conditions. The coatings will have good plasticity and"ice adhesion and provide a high degree of resistance to penetration bywater or water vapor.

The water dispersible polyvinyl acetate for formulation with dry cementis a fine dry powder containing suflicient dispersing agent to make itredispersible on addition of water. A preferred method of making waterdispersible polyvinyl acetate involves the polymerization of vinylacetate in the presence of about 6% polyvinyl alcohol based on the finalpolyvinyl acetate dry powder. The polyvinyl acetate emulsion can bespray dried-in a hot gas to produce the dry powder. However, thisinvention is not limited to any specific dispersing agent in thepolyvinyl acetate since other agents will be suitable provided they makepossible the redispersion of the powdered polymer in water.

Many formulations involving the use of water redispersible polyvinylacetate and hydraulic cement with or without other additives such aspigments are possible. The following examples will illustrate theprinciple underlying my invention.

EXAMPLE 1 The following compositions were prepared by mixing andgrinding the dry ingredients together and then adding the water withgood agitation to disperse the mixture.

Composition A Parts by weight Portland cement Hydrated lime 15 Titaniumdioxide 5 Polyvinyl acetate spray-dried emulsion 19.95 Water Totalsolids-54.3

Composition B Parts by weight Portland cement 80 Hydrated lime 15Titanium dioxide 5 Water 84 Total solids54.3%

Composition B was applied by a brush to a dry concrete surface andallowed to dry 24 hours at room temperature. Similar coatings were madeusing Composition A. The coating obtained using Composition B showedvery poor adhesion, flaking off when the surface was rubbed gently. Onthe other hand, films of Composition A exhibited excellent adhesion,withstanding scraping to eflect removal.

EXAMPLE 2 The following composition was prepared using the proceduredescribed above.

Composition C Parts by weight White Portland cement 212.5

Hydrated lime 25.0 Titanium dioxide 12.5 Polyvinyl acetate spray-driedemulsion 50.4

Water 197.0

cinder block to displace the air, then an 8-foot head of water wasapplied. The rate of seepage was determined by measusing the timeinterval required for a 12-inch dropin-headof water. Knowingthe volumeof the'water contained per inch in the glass tube above the block andthe area of the coated-cinder block, the rate of seepage could be easilycalculated. The rate was expressed in liters/ sq. ft./hour at 78 ft.head of water.

In the table are shown the results of seepage tests carried out onComposition C as well as proprietary paint of a cementitous nature.

TABLE Paint: Rate of seepage None So great, could not maintain an 8-ft.head of water. Composition C 0.143 liters/sq. ft./hr. Proprietary paintA 0.250 liter/sq. ft./hr.

It can be seen that the composition of this invention is quite effectiveas a seepage sealant.

In a very simple formulation of this invention 250 parts of a high limePortland cement, known in the trade as Brixrnent cement was mixed with500 parts of polyvinyl acetate and 150 parts of water. All parts are ona Weight basis. The rate of seepage of water for a cinder block coatedwith this composition was 0.06 liter per square foot with an 8-foot headof water.

The conditions used to spray-dry the polyvinyl acetate emulsion employedin this invention were as follows: the solids content of the emulsionwas 55% of which about 3% was polyvinyl alcohol added as a redispersingagent; inlet air temperature 850900 R; feed rate of 29 lbs. of polyvinylacetate'emulsion (dry basis) per hour; exit air temperature 130-140 F.The final 9 spray-dried product is a fine, white, free-flowing powderwith a bulk density of 0.55. A 55% solids dispersion in water has aviscosity of 980 centipoises (Brookfield) and a pH of 6.6, after beingthoroughly agitated for 30 to 60 minutes.

The spray-drying step can be accomplished at any conventional dryingtemperatures. For example, temperatures from 600 to '1000 F. maybe'used.

The amount of spray-dried polyvinyl acetate emulsion used can be variedwithin wide limits. For example, the ratio of dry polyvinyl acetateemulsion to the inorganic ingredients can vary from 1 to 1 to 1 to 10without adverse effect. However, in the preferred embodiment of thisinvention the ratio of dry polyvinyl acetate emulsion to the inorganicingredients is from 1 to 4 to l to 6 by weight.

The cement portion of the paint can consist of straight Portland cementor other hydraulic cement and may contain other modifiers includingpigments, lime and/or siliceous sand. It may also contain water-proofingsalts such as calcium stearate. The pigments which may be used includetitanium dioxide, mica, lithopone, zinc sulfide, etc. The ratio ofcement modifiers can be varied but the Portland cement content shouldnot be less than of the solids portion of the paint.

The mixtures of the dry components of any of these formulationscontaining a dry redispersible polyvinyl acetate can be storedindefinitely prior to use if kept out of contact with water.

I claim:

1. A substantially anhydrous coating composition con sisting essentiallyof one part by weight of Water dispersible polyvinyl acetate and one toten parts by weight of a hydraulic cement.

2. A substantially anhydrous coating composition con sisting essentiallyof one part by Weight of water dis persible polyvinyl acetate and one toten parts by weight of Portland cement.

3. A substantially anhydrous coating composition consisting essentiallyof more than 5% by weight .of Water dispersible polyvinyl acetate, of atleast 65% by weight of hydraulic cement and of pigment.

4. A substantally anhydrous coating composition con- I sistingessentially of more than 5% by Weight of water dispersible polyvinylacetate, of at least 65 by weight of hydraulic cement, of hydrated limeand of pigment.

5. A substantially anhydrous coating composition consisting essentiallyof more than 5% by weight of water dispersible polyvinyl acetate, atleast 65 by weight of Portland cement, of hydrated lime and of titaniumdioxide.

6. A substantally anhydrous coating composition consisting essentiallyof water dispersible polyvinyl acetate, at least 65 by Weight ofhydraulic cement and of pigment, said polyvinyl acetate comprising morethan 5% by weight of the composition.

7. A substantially anhydrous coating composition con sisting essentiallyof water dispersible polyvinyl acetate, at least 65 by weight ofPortland cement, of hydrated lime, of siliceous sand and of titaniumdioxide, said polyvinyl acetate comprising more than 5% by weight of thecomposition.

References Cited in the file of this patent UNITED STATES PATENTS1,749,923 Reardon Mar. 11, 1930 2,284,023 Scripture May 26, 19422,491,487 Faulwetter Dec. 20, 1949 OTHER REFERENCES Gregory, T. C.: Usesand Applications of Chemicals and Related Materials, Reinhold PublishingCorp., New York, N. Y. (1939), 472.

1. A SUBSTANTIALLY AHYDROUS COATING COMPOSITION CONSISTING ESSENTIALLYOF ONE PART BY WEIGHT OF WATER DISPERSIBLE POLYVINYL ACETATE AND ONE TOTEN PARTS BY WEIGHT OF A HYDRAULIC CEMENT.